Passenger conveyors such as escalators or horizontal moving walkways will typically include handrails which move along hand rail guides in synchronism with the tread portion of the passenger conveyor. The drive for the handrail can include driving rollers which engage the handrail, moving racks which engage the underside of the handrail, or rotating sprockets which engage the underside of the handrail. When driving rollers are used, they may be directly opposed to form a mangle-type nip through which the handrail moves, or they may be rectilinearly offset along the path of movement of the handrail. Driving rollers can include combinations of driven rollers and idler rollers which cooperate to move the handrail. Devices have been described in the prior art which will vary the driving force imposed upon the handrail by the driving rollers.
This provision is especially desirable when the driving rollers are smooth and rely on friction to provide the driving force necessary to move the handrail. U.S. Pat. Nos. 3,414,109 Clark, granted Dec. 3, 1968; 3,666,075 Iwata, granted May 30, 1972; 4,134,883 Mendelsohn et al, granted Jan. 16, 1979; 4,151,905 Takahashi et al, granted May 1, 1979; and 4,200,177 Sato et al, granted Apr. 29, 1980 are typical prior art disclosures of passenger conveyor handrail devices.